From VO2max + running economy (Cr) + fraction-of-VO2max → predicted finish time, pace, and running power. Per-distance plausibility checks tell you when your fraction is unrealistic for the chosen distance.
VO2max from a lab test ideally; or use a published predictor from a recent race. Cr defaults to 200 ml O2/kg/km (trained range); adjust if you have measured economy.
Three formulas turn VO2max into a finish time.
v (km/min) = VO2max × fraction / Cr
Cr = oxygen cost per km. Lower Cr = better economy = faster at the same VO2.
The % of VO2max you can hold drops with distance. ~98% at 1 km, ~85% at 5 km, ~78% at half marathon, ~73% at marathon. Auto-set by the distance dropdown.
W/kg = speed (m/s) / RE
Running effectiveness (RE) translates speed to power. Default 1.05 m/s per W/kg is the well-trained adult range.
Two athletes with identical VO2max can run very different times: a Cr of 180 vs 220 is a ~20% speed difference at the same fraction. Lab-measured Cr from a treadmill protocol is the cleanest input here. Plug measured Cr in and the predictions tighten dramatically.
If your fraction-plausibility flag goes red, your VO2max may be over-estimated, re-test, or reduce VO2max until the predicted time matches your honest race PR for that distance.
Treadmill lab test gives both directly, VO2max from gas analysis, running economy from sub-maximal stages. Plug both into this calculator and the prediction error drops from ±5% to ±2%.
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